The present invention relates to a new and improved construction of gas-blast switch of the type comprising two contact elements which can be brought into and out of engagement with one another, drive means, a pump device composed of a piston and cylinder actuatable by the switching movements of the gas-blast switch wherein during the cut-off movements of the gas-blast switch the pump device conveys an extinguishing agent out of a pump compartment through a nozzle into an exhaust or blow-off compartment, the nozzle being constructed for taking-up the switching arc formed between the separating contact elements, the piston consisting of a number of piston portions guided within one another for relative movement in a gastight fashion and dividing the piston surface or face confronting the pump compartment, one of the piston portions being positively connected with the drive means.
A gas-blast switch of the previously mentioned type is taught in Swiss Pat. No. 524,886. With this construction the piston portion positively or force-lockingly connected with the drive means is surrounded by a substantially ring-shaped auxiliary piston with which there is associated an energy storage in such a manner that during the cut-off movement the auxiliary piston carries out a pre-compression stroke under the action of the energy storage, whereas charging of the energy storage occurs during the cut-on movement by form-locking entrainment of the piston portion positively or force-lockingly connected with the drive means. With this arrangement, the ringshaped auxiliary piston is only effective prior to separation of the contacts and afterwards remains stationary. In order to be able to also extinguish relatively small currents in the presence of relatively large extinquishing distances and to obtain the pressure differential between the pump compartment and the exhaust compartment needed for extinguishing of the arc, the further moved piston surface must be sufficiently large in size. This relatively large piston surface required for cutting-off small currents, during the cutting-off or relatively large currents requires considerable drive power because the nozzle in the presence of such large currents is clogged by the arc burning therein and which possesses a relatively large diameter, and thus permits of only a very small quantity of gas to flow therethrough. Due to the clogged nozzle the pressure then increases in the pump compartment, resulting in an increase of the aforementioned required drive power. If, in these situations, there is not available the necessary drive force or power then the piston portion or section positively or force-lockingly connected with the drive means and thus also the contact element connected therewith is moved back, in other words in the cut-on direction. Hence, the cut-off movement is retarded. With this movement hot gases additionally flow out of the nozzle back into the pump compartment, and the gas seal in the pump compartment decreases. If the extinguishing gas in the pump compartment possesses a smaller density then the extinguishing characteristics of the gas-blast switch are unfavorably impaired. This gas-blast switch only can be operationally reliably actuated with a relatively large and economically unfavorable drive means.